The speed and power requirements of microelectronic devices, e.g. capacitors, supporting substrates and connectors, and the like are critically dependent on the dielectric properties of the materials of construction of such devices. For instance, the net speed of a microelectronic device is equivalent to the sum of all the circuit delays. A major source of circuit delay is the time required for an electrical pulse to travel between gates. For a bipolar circuit the propagation velocity is inversely proportional to the square root of the dielectric permittivity of the substrate, which is often a polymeric material. Thus, reducing the permittivity of the substrate results in an increased device speed or an expansion of the circuit dimensions without a loss in speed. The reduced capacitance associated with circuit traces allows a closer spacing of circuit elements without excessive levels of crosstalk. Reduction of line capacitance also directly reduces power consumption, which in turn reduces the heat output of the device.
High performance polymers are finding expanded uses in electrical and electronic devices owing to the ease of fabrication of parts from such polymers and the favorable balance of properties such as low weight, high temperature resistance, solvent resistance, high tensile strength, low moisture absorption and low dielectric permittivity. Typical flexible printed circuit interconnections are fabricated from polyimides, polyesters, fluoropolymers and reinforced epoxy laminates. Only the fluorocarbons have relatively low permittivity, e.g. about 2. The fluorocarbons, however, suffer from two main limitations, e.g. low melting point (typically less than 260.degree. C.) and poor dimensional stability. The other polymeric materials typically have permittivities of about 3 or higher. In the case of polyimides the dielectric permittivity can be as low a about 2.8 when dry; however due to the tendency to absorb moisture the permittivity will rise to about 3.2 with moisture absorption.